$=-2 a x+4 b x^{3}=x\left(4 b x^{2}-2 a\right)=0$

$x_{1}=0$

$x_{2}=\sqrt{a / 2 b}$

$F=-k x$

$\frac{d F}{d x}=k=\frac{d^{2} V(x)}{d x^{2}}$

$k=\frac{d}{d x}\left(-2 a x+4 b x^{3}\right)=-2 a+12 b x^{2}$

$k(x=0)=-2 a$

$k(x=\sqrt{a / 2 b})=-2 a+6 a=4 a$

$\omega=\sqrt{\frac{k}{m}}$

$\omega=\sqrt{\frac{k}{m}}=\sqrt{\frac{4 a}{m}}$

$\omega=2 \sqrt{\frac{a}{m}}$